An area of continuing research in aircraft design stems from the desire to decrease the minimum landing and takeoff distances of aircraft. Many remote locations are inaccessible to relatively large aircraft due to economic circumstances for physical geography which prevent construction of conventional landing fields. Thus a need has always existed for providing relatively large aircraft that are capable of taking off and landing in confined locations.
Since the 1940's a variety of aircraft have been developed with means for directing airflow downwards in order to increase lift at low air speeds. One way of increasing aircraft lift is to provide trailing edge wing flaps that are deployed at takeoff and landing in order to extend aircraft wing surface. These trailing edges flaps need to be of considerable size on larger aircraft to successfully increase lift. Such large trailing edge flaps require substantial linkages for their support and to control their motion during flight.
An example of linkages used with trailing edge wing flaps on short takeoff and landing aircraft can be found in U.S. Pat. No. 3,874,617 to Johnson. The Johnson device discloses a double four bar linkage for flap actuation with an interconnecting linkage for deflecting the spoiler as the flap is extended. The spoiler thus serves as a third flap with its downward deflection proportional to flap extension at takeoff and landing. The Johnson device has proven to be an adequate mechanism and an improvement in the art for small to medium size aircraft.
Several problems arise, however, when trying to adapt the Johnson linkage to a larger cargo or passenger aircraft. A significant problem is due to insufficient rigidity. This type of multipiece linkage lacks sufficient rigidity to control flap movement and vibration in larger aircraft. As a large flap is deployed from a swept wing aircraft the inboard and outboard ends of the flap move away from the wing at varying rates due to the aerodynamically dictated variation in flap size with increasing distance from the fuselage. This requires such linkages to move sideways during extension of the flap and as a result multipiece linkages cannot be made rigid for this application. In order to accommodate such sideways movement without bending a relatively large amount of play (looseness) is allowed in the linkage. Typically, several linkages are used to move the flap. Play in the linkages results in substantial wear and increases maintenance work due to uncontrolled movement and chaffing between parts.
Another aspect of short takeoff and landing aircraft design to be considered is use of high lift flaps in redirecting the engine exhaust thrust. The flap must therefore be strong enough to withstand the impact of engine thrust without sustaining damage or jamming.
In view of the above a need exists for a means of providing an adjustable flap system for large aircraft capable of withstanding increased load requirements due to increased aircraft weight and the application of engine thrust. This need implies a further need for increased flap rigidity to reduce flap maintenance and structural wear.
In view of the above it is object of this invention to provide an improved trailing edge flap system for relatively large short takeoff and landing (STOL) aircraft.